Does anyone know what the thing is underneath the oil filter? It's on the bottom of the filter assembly, looks like its plastic and looks like it should unscrew and coke off.. my book doesn't say anything about it... Go figure... Thanks

Does anyone know what the thing is underneath the oil filter? It's on the bottom of the filter assembly, looks like its plastic and looks like it should unscrew and coke off.. my book doesn't say anything about it... Go figure... Thanks